This invention relates to a d-c motor control circuit and more specifically relates to a novel H-bridge driver for controllably driving loads such as d-c motors.
Control circuits are well known for driving d-c motors. H-bridge circuits are commonly employed which employ two high side MOSFETs and two low side MOSFETs in which each high side device is in series with a respective low side device. The nodes between the pairs of high side and low side devices, hereinafter M1 and M2 respectively, are connected to the motor terminals; the drains of each of the high side devices are connected to a d-c source such as a battery, hereinafter Vcc, and the sources of each of the low side devices are connected to ground (hereinafter GND).
A control circuit is then provided to turn the high side and low side devices on and off to drive current through the motor windings in directions to cause rotation of the motor rotor in a clockwise or counterclockwise direction.
The MOSFETs used for such circuits are commonly individually mounted as discrete devices; and the control circuits for controlling their conduction have also been formed of discrete circuits or combinations of several integrated circuits and discretes. Further, complicated programmed circuits have also been necessary to the circuit control. All of this increases complexity and cost and reduces reliability of the control.
It would be desirable to reduce the component count of such circuits; and to simplify their operation and to avoid the need for programmed control functions.
In accordance with the invention, a novel fully protected dual high side switch IC is provided with two additional discrete low side switches. The two high side switches and the control IC for controlling their operation may be contained on a common heat sink in a single plastic package having suitable connection pins for connection to the d-c source, ground, the motor terminals and the microcontroller which commons particular motor operations. Pins are also provided for an RC control circuit which controls soft start independently of signals from the microcontroller.
The single high side package drives and controls the entire H-bridge circuit, and contains a number of novel features.
The input signals IN1 and IN2 to the two high side FET drivers to be later described are also shown for explanatory purposes, as applied to the two high side FETs (in FIG. 1) and operate to select the motor operation modes and provide the control within each mode. First a novel self adaptive shoot thru prevention circuit (during turn off) is provided to prevent the simultaneous conduction of a series connected (half-bridge) high side MOSFET and low MOSFET. In accordance with this feature, the low side driver circuits are contained in the integrated control circuit mounted with the high side devices. The low side FETs both always normally conduct to lock the motor when the circuit is off. To turn off, the high side MOSFETs are turned off by IN1 or IN2 which turns on the low side driver circuit of its respective low side FET to turn it on before the slower high side MOSFET turns fully off, particularly when its output voltage reaches and exceeds a small value, for example, 2 volts. More specifically, to turn off a high side MOSFET, the high side FET is turned off and the circuit waits until its output voltage is less than about 2 volts. The low side FET which is off is then turned on to lock the motor load. Thus, shoot thru protection is adaptively provided without the conventional dead-time control circuit.
Second, a novel soft start sequence is provided each time the motor restarts, as selected by the IN1 and IN2 signals. The soft start circuit employs a PWM sequence which cycles a corresponding one of the low side switches to which current is steered by one of the high side switches (MOSFETs). This limits motor in rush current. The soft start sequence is operated (programmed) by a simple RC circuit and is automatically reset after starting.
Third, the novel circuit provides over current(short-circuit) and over temperature (overload) protection under the control of the IC in the high side MOSFET package. These protective functions are carried out by current sensors and thermal sensors on the high side MOSFETs, which are xe2x80x9cIPSxe2x80x9d switches, and provide a status feed-back to the microcontroller to call for shut-down. The protective circuit is then reset when IN1 and IN2 are both low (or zero).
Fourth, a number of other functions are carried out within the single control IC, which are selected by the combinations of signals IN1 and IN2; for example, under-voltage lockout; motor braking, temperature protection and the diagnostic feedback.